AUTHOR AND EDITOR INFORMATION

Section 1 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

INTRODUCTION

Section 2 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Background

Megaloblastic anemias are a heterogeneous group of disorders that share common morphologic characteristics. Erythrocytes are larger and have higher nuclear-to-cytoplasmic ratios compared to normoblastic cells. Neutrophils can be hypersegmented, and megakaryocytes are abnormal. On the molecular level in megaloblastic cells, the maturation of nuclei is delayed, while cytoplasmic development is normal.

Megaloblastosis is a generalized disorder because nonhematopoietic cells, such as gastrointestinal and uterine cervical mucosal cells, can also have megaloblastic features. The etiology of megaloblastic anemias is diverse, but a common basis is impaired DNA synthesis. The most common causes of megaloblastosis are cobalamin (vitamin B-12) and folate deficiencies. The usual causes of cobalamin deficiency are pernicious anemia (PA, see Pernicious Anemia), failure of absorption of cobalamin in the terminal ileum, and the effects of medications. Folate deficiency is usually due to folate-poor diets but may also occur in patients with tropical sprue, in patients who are pregnant, and in patients on antifolate or other medications. Current routine folate replacement during pregnancy and folate-containing multivitamin supplementation for elderly persons has led to a decline in the frequency of folate deficiency.

Some patients can be asymptomatic. The development of megaloblastic anemia is usually insidious; therefore, patients are often relatively asymptomatic because they have had time to adjust to the marked fall in hemoglobin (Hgb) levels. Patients with cobalamin deficiency may develop debilitating neurological impairment that may develop independently of anemia.

Recent trends in medical care have emphasized early therapy. Folate supplementation is recommended to prevent the atherosclerosis and thromboembolic events by reducing homocysteine levels. Folate is given during pregnancy to prevent developmental defects in the fetus. Mild cobalamin deficiencies and incipient cobalamin-related neuropsychiatric abnormalities have recently been identified in some individuals, and prompt early treatment with cobalamin is recommended to avoid progression of mental deterioration and neurological complications. A recent review focuses on the relation between various outcomes of human reproduction (ie, pregnancy, lactation, and male reproduction) and folate nutrition and metabolism, homocysteine metabolism, and polymorphisms of genes that encode folate-related enzymes or proteins (Tamura, 2006).

Pathophysiology

The molecular basis for megaloblastosis is a failure in the synthesis and assembly of DNA. The most common causes of megaloblastosis are cobalamin and folate deficiencies. Cobalamin metabolism and folate metabolism are intricately related, and abnormalities in these pathways are believed to lead to the attenuated production of DNA.

Methotrexate-induced megaloblastosis has been ascribed to a deficiency in deoxythymidine triphosphate (dTTP) that is consumed by the methyl folate trap. Evidence exists that megaloblastosis is caused by interference of folate metabolism by the inhibition of methionine synthesis. However, because of dietary folate deficiency, the size of the dTTP pool is normal or increased in persons with megaloblastosis.

Impairment in the deoxyuridine monophosphate (dUMP) ¡ú deoxythymidine monophosphate (dTMP) pathway may be responsible for nutritional megaloblastosis. Despite this information, the biochemical basis for megaloblastosis is not fully understood. This is especially true of the cobalamin-related neuropathy that can occur independently of megaloblastic changes in hematopoietic cells. One hypothesis for the cause of cobalamin neuropathy is that a defect exists in the conversion of adenosyl-cobalamin-dependent conversion of methylmalonyl coenzyme A to succinyl coenzyme A.

A hallmark of megaloblastic anemia is ineffective erythropoiesis, as evidenced by erythroid hyperplasia in the bone marrow, a decreased peripheral reticulocyte count, and an elevation in lactate dehydrogenase (LDH) and indirect bilirubin levels. The pathogenesis of these findings is the intramedullary destruction of fragile and abnormal megaloblastic erythroid precursors.

An understanding of the source of cobalamin and folate is important to understand the pathogenesis of the development of megaloblastosis. Dietary intake is the source of cobalamin and folate because humans cannot synthesize these substances. Cobalamin must be bound to intrinsic factor (IF), and this complex is taken up in the terminal ileum. Once absorbed, cobalamin is bound to another protein, transcobalamin II (TCII), and is transported to storage sites. Abnormalities in any of these steps in cobalamin transport can lead to deficiencies in this substance. Considerable amounts of cobalamin are accumulated in storage sites; this explains why years elapse before cobalamin deficiency develops in patients who cannot take up dietary cobalamin.

Although the processing and transport of ingested folate is complex, folate-induced megaloblastosis is rarely caused by abnormalities in transport but instead is most often caused by dietary insufficiency. Folate deficiency can be caused by malabsorption in patients with sprue. In contrast to cobalamin, very little folate is stored; this explains why folate deficiency can occur within months of cessation of folate ingestion.

Megaloblastosis can also be caused by disorders in which cobalamin and folate uptake and metabolism are not affected. Myeloproliferative syndromes and viral infections (eg, HIV) can lead to megaloblastosis by disrupting DNA synthesis. Megaloblastosis can occur in patients who are on certain medications, including many cancer chemotherapy drugs.

Frequency

United States

Because the etiology is diverse, determining a numerical estimate of the frequency of megaloblastic anemias is difficult.

Dietary and pregnancy-related folate deficiencies are probably the most common causes of megaloblastic anemias. However, current folate supplementation during pregnancy and vitamin supplementation for elderly persons has resulted in a low frequency of these forms of megaloblastosis.

Megaloblastosis may be caused by a small number of drugs, for instance antifolates such as methotrexate, purine analogues such as azathioprine, pyrimidine analogs such as 5-fluorouracil, ribonucleotide reductase inhibitors such as hydroxyurea, anticonvulsants such as phenytoin, and oral contraceptives.

The frequency of pernicious anemia is 0.25-0.5 cases per 1000 persons in their seventh decade of life. Other forms of megaloblastosis are rare.

International

The frequency of PA is reported to be higher in Sweden, Denmark, and the United Kingdom (100-130 cases per 100,000 population). Note that the frequency of megaloblastosis is highest in countries in which malnutrition is rampant and routine vitamin supplementation for elderly individuals and pregnant women is not available.

Mortality/Morbidity

The major morbidity of cobalamin deficiency is related to the severity of the anemia. In cobalamin deficiency, neurological impairment and anemia are major complications. Recent studies indicate that folate deficiency may also lead to neurological impairment. Megaloblastic anemia is more likely to be detected and treated in most industrial and Western nations. Therefore, the morbidity and mortality due to megaloblastosis have been reduced.

• Neurological impairment can occur in patients who are not anemic. The inadvertent treatment of patients with cobalamin deficiency with folate corrects the anemia but will not halt the progression of the neurological disorder. Therefore, neurological impairment continues to be a problem in some patients with cobalamin deficiency.
• Evidence suggests that folate deficiency during pregnancy can lead to neural tube defects and other development disorders in the fetus. However, folate supplements during pregnancy have reduced this morbidity.

Race

Older literature indicated that pernicious anemia occurs primarily in white persons and is more likely to occur in persons of Scandinavian descent and others of northern European descent. Recent evidence suggests that pernicious anemia also occurs in Asian and African American persons, although with much lower frequency.

Age

Pernicious anemia usually occurs in individuals older than 40 years, and the prevalence increases in older populations. Dietary folate deficiency also increases in older populations because of poor diets. Boiling foods in water dilutes folates, and excessive heating destroys folates.

CLINICAL

Section 3 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

History

Anemia is a common feature of all megaloblastic anemias. However, most patients are relatively asymptomatic because anemia usually develops slowly. Therefore, the absence of symptoms of anemia does not exclude the diagnosis of megaloblastosis. When a marked decrease in Hgb occurs, patients can present with dyspnea, light-headedness, palpitations, and heart failure. Patients with cobalamin deficiency can present primarily with neurological impairment. Specific aspects of the etiology of cobalamin and folate deficiencies are described below.

• When obtaining a history with findings of possible cobalamin deficiency, obtaining evidence of anemia and neurological impairment first is important.
• • Some patients can have gastrointestinal symptoms such as loss of appetite, weight loss, nausea, and constipation.
  • Patients may have a sore tongue and canker sores.
  • Patients may have symptoms of anemia.
  • Early neurological symptoms include paresthesias in the feet and fingers, poor gait, and memory loss. At later stages, patients can have severe disturbances in gait, loss of position sense, blindness due to optic atrophy, and psychiatric disturbances. In some patients, neurological impairment can occur without anemia. Therefore, neurological symptoms may range from mild to severe, and cobalamin deficiency should be considered even with minimal neurological symptoms and the absence of anemia.
• In the next phase of eliciting relevant history, obtaining a history that can help distinguish between the causes, such as inadequate diets, malabsorption, medications, and congenital disorders, is important.
• • A history of folate administration without vitamin B-12 therapy should be documented because folate may partially correct hematological abnormalities but will not stop the progression of neuropsychiatric complications.
  • Dietary insufficiency of cobalamin is a rare cause of megaloblastosis. A history of a long-standing vegetarian diet without dairy products or eggs can suggest the possibility of this etiology.
  • Pernicious anemia is associated with autoimmune disorders. A coexistent history of autoimmune disorders such as thyroid disorders, type I diabetes, Addison disease, hypoparathyroidism, or autoimmune hemolytic anemia suggests the possibility of pernicious anemia.
  • A history of a gastrectomy suggests the possibility of cobalamin deficiency. Approximately 3-5 years must elapse for cobalamin deficiency to occur after total gastrectomy and approximately 12 years must elapse after partial gastrectomy.
  • A history of ileal resection, regional ileitis, and small intestinal lymphoma suggests intestinal malabsorption of cobalamin.
  • Previous gastric or intestinal surgery may also suggest the possibility of blind loop syndrome.
  • Zollinger-Ellison syndrome can cause megaloblastosis.
  • Handling or eating raw fish tapeworm suggests that the entrenchment of the tapeworm in the small intestine may be responsible for cobalamin deficiency.
  • A history of taking medications mentioned in Causes or exposure to nitrous oxide may suggest cobalamin deficiency.
  • A history of megaloblastosis since childhood suggests a congenital cause of cobalamin deficiency.
• Obtaining a history in support of folate deficiency should focus on the patient's diet, evidence of increased folate turnover and consumption, indications of malabsorption and sprue, pregnancy, and medications.
• • Folate deficiency develops rapidly because folate stores are minimal.
  • Folate deficiency manifests primarily as anemia, but recent evidence indicates that folate deficiency may also lead to neurological syndromes.
  • Dietary insufficiency is the most common cause of folate deficiency. A typical patient is an elderly person whose diet is inadequate or who cooks foods diluted in water with excessive heat. Dilution and heating can destroy folate. Alternative diets that are low in folate can produce folate deficiency.
  • Impaired absorption may result in folate deficiency. Nontropical sprue should be considered in patients who have megaloblastosis and symptoms of malabsorption, such as weight loss, abdominal distention, diarrhea, and steatorrhea. These patients often have metabolic bone disease or bleeding due to deficiencies in vitamin K–dependent factors. They may describe a sensitivity to gluten. Megaloblastosis may not be evident because of the superimposed iron deficiency.
  • Tropical sprue can cause folate deficiency. In addition to signs of malabsorption, these patients have a history of living or visiting tropical regions. Tropical sprue may develop years after the patients visited the tropics.
  • Other intestinal disorders that may cause megaloblastosis as a result of folate malabsorption may include regional enteritis, intestinal lymphoma, surgical intestinal resection, amyloidosis, Whipple disease, and scleroderma.
  • Increased folate requirements can occur during pregnancy because of transfer of folate to the fetus and during lactation. Dilantin therapy increases the requirement for folate. Patients with psoriasis and exfoliative dermatitis require additional folate because of the increased turnover of epidermal cells.
  • Miscellaneous causes of folate deficiency can occur during hyperalimentation and hemodialysis because folate is lost in dialysis fluid. Megaloblastosis in persons with alcoholism is often due to coexistent folate deficiency.
  • A history of drugs and antifolate agents mentioned in Causes should be elicited because these agents can cause folate deficiency.
  • Folate deficiency can occur in infants who are fed goat milk (low folate content). Infants who are on synthetic diets for congenital disorders can develop folate deficiency. Premature infants can develop folate deficiency in the presence of infection or diarrhea.
• A lifelong history of megaloblastosis or folate deficiency suggests a congenital disorder.
• A history of HIV infection or a myelodysplastic syndrome may suggest that megaloblastosis is due to a direct effect of these disorders on bone marrow stem cells.

Physical

The physical examination may reveal findings indicative of the consequences of anemia in most persons with megaloblastic anemias.

• Neuropsychiatric signs are usually found only in patients with cobalamin deficiencies.
• Findings may indicate predisposing conditions or underlying disorders. For example, signs of autoimmune disorders that are associated with PA may be detected.
• Physical examination findings may range from barely detectable to markedly abnormal.
• Evidence of malabsorption indicates that the patient has sprue.
• Patients may have a lemon-yellow hue due to the combination of anemia and an increased level of indirect bilirubin. When the decrease in the Hgb level is severe, evidence of an uncompensated anemia is present, such as tachycardia and dyspnea. In many cases, the fall in the Hgb level is moderate and develops slowly; therefore, patients have compensated anemias characterized only by weakness.
• Glossitis, characterized by a smooth tongue due to loss of papillae, occurs in persons with cobalamin deficiency.
• Dermatological signs include hyperpigmentation of the skin and depigmentation of the hair because of increased melanin synthesis.
• Neurological signs occur primarily in persons with cobalamin deficiencies but may also occur in persons with folate deficiency. The signs can vary from minimal to severe. Peripheral neuropathy, abnormal gait, loss of balance, loss of proprioception and vibratory senses, blindness due to optic atrophy, depression, loss of memory, and psychiatric disorders may occur.
• Neuropsychiatric complications of folate deficiency are usually limited to irritability and minimal changes in personality.
• Abdominal scars may be evident from gastrectomies, ileal resections, or other procedures that may lead to blind loop syndrome.
• When cobalamin deficiency is caused by lack of absorption in the terminal ileum due to regional ileitis, physical evidence of this disorder may be present.
• Patients with pernicious anemia may have signs of autoimmune disorders, including thyroid disorders, type I diabetes, and autoimmune hemolytic anemias.
• Patients with nontropical and tropical sprue may have signs of malabsorption such as weight loss, abdominal distention, diarrhea, and steatorrhea. These patients often have metabolic bone disease or bleeding due to deficiencies in vitamin K–dependent factors.
• Patients who have megaloblastosis due to HIV infection or myelodysplastic syndromes usually have signs of these disorders.
• Children with inborn errors that cause folate and cobalamin deficiencies or inborn errors that have a direct effect on stem cells may have signs of these congenital disorders.

Causes

Megaloblastic anemias can be caused by cobalamin deficiency or folate deficiency. Disorders such as myeloproliferative syndromes can disrupt DNA synthesis directly. Many pharmaceutical agents also interfere with DNA synthesis and cause megaloblastic changes in hematopoietic and other frequently dividing cells. The causes are diverse and are discussed below.

• Cobalamin (vitamin B-12) deficiency can be caused by impaired gastric or intestinal absorption, inadequate dietary intake, drugs, or congenital errors in metabolism.
• • Nutritional deficiency: This is a rare etiology, but it can occur in individuals who are on vegetarian diets without milk, cheese, and eggs over a number of years because depletion of cobalamin reserves stored in the liver takes years.
  • Food-cobalamin malabsorption: This is characterized by the inability to release cobalamin from food, possibly because of gastric anacidity. As a result, cobalamin cannot bind to intrinsic factor (IF) and cannot be taken up. This entity has been recognized recently, and its prevalence as a cause of megaloblastosis requires further study.
  • Pernicious anemia: This is the best-known cause of cobalamin deficiency. This disorder results from the absence of functional IF, which leads to impaired gastric absorption of cobalamin. In most cases, the loss of functional IF is caused by the autoimmune destruction of gastric parietal cells. However, some cases of pernicious anemia can be traced to a hereditary lack of production of IF.
  • Gastrectomy: Patients develop pernicious anemia following gastrectomy because of the lack of a source of IF. Development of overt megaloblastosis requires approximately 3-5 years following total gastrectomy and approximately 12 years following partial gastrectomy. The lag is because of the time required to deplete cobalamin stores.
  • Zollinger-Ellison syndrome: In this disorder, the secretion of large amounts of acid cannot be neutralized by pancreatic secretions. Therefore, the persistent acidity inactivates pancreatic proteases in the duodenum and prevents transfer of cobalamin from r-factor to IF. This factor (r-factor) is a cobalamin binder secreted by salivary glands.
  • Severe abnormalities in the terminal ileum due to ileal resection, regional ileitis, or lymphoma: The terminal ileum is the site of uptake of cobalamin-IF complexes; therefore, these disorders can lead to cobalamin deficiencies. Several years are required for cobalamin deficiency to occur following the onset of these disorders because of the time required to deplete cobalamin reserves.
  • Diphyllobothrium latum (ie, fish tapeworm): When the tapeworm is entrenched in the small intestine, it competes with the host for ingested cobalamin. The organism is most often found in Canada, Alaska, and the Baltic Sea.
  • Blind loop syndrome: This syndrome involves bacterial colonization of intestines that are either deformed because of strictures, surgical blind loops, or anastomoses or abnormal because of scleroderma or amyloidosis. Bacteria compete with the host for cobalamin.
  • Nitrous oxide: Methyl chloride is destroyed rapidly after prolonged exposure to nitrous oxide and can produce megaloblastosis.
• Folate deficiency can be due to dietary deficiency, lack of absorption, or increased folate consumption. In contrast to cobalamin deficiency, folate deficiency develops rapidly because folate stores are minimal.
• • Folate depletion: This usually occurs because of dietary insufficiency, the destruction of folate by excessive heating of diluted foods, or consuming alternative diets that are low in folate.
  • Impaired absorption: These patients often have metabolic bone disease or bleeding due to deficiencies in vitamin K–dependent factors. They may describe a sensitivity to gluten. Megaloblastosis may not be evident because of superimposed iron deficiency.
  • Tropical sprue: Tropical sprue has a more severe effect on the distal ileum than nontropical sprue. Therefore, tropical sprue can lead to cobalamin deficiency and folate deficiencies.
  • Other intestinal disorders: Megaloblastosis can occur because of folate malabsorption in patients with a history of regional enteritis, intestinal lymphoma, surgical intestinal resection, amyloidosis, Whipple disease, and scleroderma.
  • Increased turnover or requirements: This can occur during pregnancy because of the transfer of folate to the fetus and during lactation. Dilantin therapy increases the requirement for folate. Patients with psoriasis and exfoliative dermatitis require additional folate because of the increased turnover of epidermal cells.
  • Infants: Folate deficiency can occur in infants on a diet of goat milk (low folate content), premature infants with infection or diarrhea, and infants on synthetic diets for congenital disorders.
  • Miscellaneous: Folate deficiency can occur during hyperalimentation and hemodialysis because folate is lost in dialysis fluid. Megaloblastosis in persons with alcoholism is often due to folate deficiency.
• Drugs that can cause megaloblastic anemia are as follows:
• • Antifolates - Methotrexate, aminopterin
  • Purine analogs - 6-Mercaptopurine, 6-thioguanine, acyclovir
  • Pyrimidine analogs - 5-Fluorouracil, 5-azacytidine, zidovudine
  • Ribonucleotide reductase inhibitors - Hydroxyurea, cytarabine arabinoside
  • Anticonvulsants - Phenytoin, phenobarbital, primidone
  • Other drugs that can depress folates - Oral contraceptives, glutethimide, cycloserine
  • Drugs that affect cobalamin metabolism - p-Aminosalicylic acid, metformin, phenformin, colchicine, neomycin, biguanides
• Megaloblastic anemia in children can be caused by the following:
• • Inborn errors of cobalamin metabolism
  • • Selective malabsorption of cobalamin with normal secretion of IF (Imerslünd-Grasbeck syndrome).
    • Other causes are congenital IF deficiency, TCII deficiency, r-binder deficiency
    • Methylmalonic aciduria
    • Homocystinuria
    • Methylmalonic aciduria and homocystinuria
  • Inborn errors of folate metabolism
  • • Congenital folate malabsorption
    • Dihydrofolate reductase deficiency
    • N⁵-methyl tetrahydrofolate - Homocysteine methyltransferase deficiency
  • Other inborn errors
  • • Hereditary orotic aciduria
    • Lesch-Nyhan syndrome
    • Thiamine-responsive megaloblastic anemia - This condition is an autosomal recessive disorder with features that include megaloblastic anemia, deafness, and diabetes mellitus. Thiamine uptake into cells is disturbed, and treatment with pharmacological doses of thiamine ameliorates the megaloblastic anemia and diabetes mellitus.
  • Neoplastic or viral infections (eg, myelodysplastic syndromes, other clonal neoplastic diseases) and HIV infections - Can directly affect bone marrow stem cells

DIFFERENTIALS

Section 4 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Other Problems to be Considered

Occasionally, the morphological changes in megaloblasts and other cells may be extremely bizarre; these changes have been misinterpreted as neoplasia, acute leukemia, or myelodysplasia.

WORKUP

Section 5 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Lab Studies

• A CBC count, RBC indices, platelet count, differential count, reticulocyte count, and microscopic examination of the peripheral blood smear should be performed.
• • A typical patient with megaloblastic anemia presents with macrocytic anemia with thrombocytopenia and a decreased reticulocyte count. The mean cell volume can range from 100-150 fL or greater.
  • Hypersegmented neutrophils can be observed on the peripheral smear and represent an early phase of megaloblastosis in persons with nutritional megaloblastic anemias. Hypersegmented neutrophils contain 5 or more lobes, while normal neutrophils contain 3-4 lobes.
  • Macrocytes are oval and have been called macroovalocytes. In persons with severe anemia, macrocytes with nuclear remnants and erythrocytes with megaloblastic nuclei can be present in the peripheral blood. Macrocytes can be found in the peripheral blood in patients with liver disease or hemolytic anemia (because of an increase in reticulocytes) and usually do not have oval features. However, macroovalocytes are characteristic of megaloblastic anemias.
  • In general, the profoundness of megaloblastic changes is proportional to the severity of the anemia.
  • In some cases of megaloblastosis, no anemia is present despite overt neuropsychiatric disease. One cause of this disparity is the administration of folic acid to patients with cobalamin deficiency. This therapy partially corrects the anemia, but the neuropathy is not affected and progresses.
  • Macrocytosis due to cobalamin or folate deficiencies may be masked in patients with microcytic anemias because of thalassemia or iron deficiency. However, hypersegmentation of neutrophils may persist. Transfusion therapy or infections may modify the expression of megaloblastosis.
• LDH and indirect bilirubin assays should be ordered, and results are expected to be high because of intramedullary destruction of megaloblastic red cell precursors. LDH fraction 1 (LDH₁) and LDH fraction 2 (LDH₂) are elevated, with LDH₁ being greater than LDH₂. The LDH level is often extremely high, and, following therapy, the fall in the LDH level is an excellent indication of response to or failure of therapy. Increased LDH and indirect bilirubin levels along with a decreased reticulocyte count suggest ineffective hemopoiesis in which intramedullary hemolysis is occurring.
• Serum iron and ferritin assays should be ordered initially and during the treatment of megaloblastic anemias. These parameters may be high. Increased iron turnover occurs in persons with untreated megaloblastosis. However, serum iron and ferritin levels may also decrease because patients respond to therapy and consume iron stores for the production of new RBCs. If iron stores are depleted, patients have an incomplete response to cobalamin or folate therapy.
• Tests for the diagnosis of cobalamin deficiency are described as follows:
• • The most important test is measuring the serum cobalamin level. In a typical clinical presentation of megaloblastic anemia, a low serum cobalamin level and a full response to cobalamin may be sufficient to establish a diagnosis. A Schilling test can be performed in patients who have been treated with cobalamin and folate. This test can be used to diagnose cobalamin deficiency and to distinguish between pernicious anemia and ileal malabsorption.
  • Serum for cobalamin levels should be drawn before transfusions or vitamin B-12 therapy. If the test cannot be performed within a reasonable time frame, serum should be frozen to preserve it for testing so that therapy can be started. Serum cobalamin levels are usually low in patients with anemia due to cobalamin deficiency. However, exceptions to this rule exist.
  • Cobalamin levels may be falsely high in patients with megaloblastosis due to nitrous oxide, TCII deficiency, inborn errors in cobalamin metabolism, and myeloproliferative disorders. On the other hand, serum cobalamin levels can be falsely low with normal tissue levels in some patients with folate or iron deficiency, vegetarians, individuals on high doses of ascorbic acid, pregnant women, and persons with transcobalamin I (TCI) deficiency.
  • Serum samples for folate levels should also be obtained and, if necessary, frozen prior to therapy in patients with possible cobalamin deficiency because patients with folate deficiency can have reduced cobalamin levels.
  • A Schilling test is a radiometric test of cobalamin absorption. The test is given in 3 parts, as follows:
    • In the first part of the test, radioactive cyanocobalamin is given orally. Unlabeled cyanocobalamin is given intramuscularly to inhibit the uptake of radioactive cobalamin by the liver. Next, the urinary secretion of radioactive cobalamin is measured to estimate whether the orally administered cobalamin has been taken up. Low secretion suggests either pernicious anemia or an abnormality in the terminal ileum that prevented the uptake of IF-cobalamin complexes.
    • The second part of the test is performed in the same manner, except that IF is given orally along with radioactive cyanocobalamin. If IF restores the uptake of ingested radioactive cyanocobalamin, the patient most likely has pernicious anemia. However, if IF does not restore uptake, then an abnormality in the terminal ileum is most likely present.
    • A third phase can be performed in which the patient is treated with antibiotics prior to administering radioactive cyanocobalamin. If antibiotics restore cobalamin absorption from the gastrointestinal tract, the patient most likely has a blind loop syndrome.
    • The main difficulty with the Schilling test is inadequate collection of urine samples in patients who are either noncompliant or in renal failure.
    • The results of the Schilling test may indicate cobalamin malabsorption in patients who have severe and long-standing folate deficiencies. This is because of the effect of severe folate deficiency on the ileal mucosa that leads to a decrease in cobalamin uptake in the terminal ileum. Treating patients with severe folate deficiency with both cobalamin and folate for a month may be advisable to restore the ileal mucosa before performing a Schilling test.
  • A protein-bound absorption test (also known as food-cobalamin absorption test) should be performed if food-cobalamin malabsorption is suggested. In this disorder, IF is present, but cobalamin bound to r-binder is not released and thus cannot bind to IF. Results of a standard Schilling test are normal in persons with this disorder. However, if the Schilling test is modified by using in vivo cyanocobalamin-radiolabeled food or in vitro cyanocobalamin-radiolabeled chicken serum or eggs instead of free radiolabeled cyanocobalamin, the Schilling test result will be abnormal. The results of the modified Schilling test can help detect the failure of the release of cobalamin bound to foods.
  • Methylmalonic aciduria is another test. Urinary excretion is a reliable index of cobalamin deficiency, provided the patient does not have renal failure.
  • Serum methylmalonic acid and homocysteine test results are elevated in more than 90% of patients with cobalamin deficiencies.
  • Antiparietal cell antibodies are rarely ordered in current practice. Of patients with pernicious anemia, 90% are positive for these antibodies. However, antiparietal cell antibodies are also present in patients with thyroid disease and other autoimmune disorders.
  • Anti-IF antibodies (type I and II) are highly specific for pernicious anemia. However, tests for these are rarely ordered to diagnose or treat patients with megaloblastosis.
• Tests for folate deficiency
  • Serum folate is the earliest indicator of folate deficiency. Serum samples should be collected prior to therapy or transfusions. If necessary, serum can be frozen until the laboratory can perform the test. Folate levels respond rapidly to changes in dietary folate. A low folate level reflects dietary intake during the previous 2-3 days. Conversely, a single meal with normal folate content can restore serum folate levels to normal.
  • The RBC folate level is usually low in patients with folate deficiency. Folate is incorporated into erythrocytes when they are formed, and folate levels do not fluctuate with changes in diet during the lifespan of the RBC. The RBC folate level may not be low in persons with rapidly developing acute folate deficiency. Another limitation of this test is that RBC folate levels are low in more than 50% of patients with cobalamin deficiency, and this test cannot be used to distinguish between these disorders.

Imaging Studies

• Abdominal x-ray films, upper and lower GI series, and CT scans may be useful for detecting and evaluating blind loop syndromes, strictures, and other gastrointestinal tract abnormalities that may cause a blind loop syndrome.

Other Tests

• Cobalamin deficiency - Detection and evaluation of autoimmune disorders, regional ileitis, fish tapeworm infection, Zollinger-Ellison syndrome, pancreatitis, and myeloproliferative disorders
• Folate deficiency - Detect and evaluate pregnancy, malnutrition, and other complications of sprue, chronic hemolysis, and exfoliative dermatitis
• Tests relevant for the diagnosis and evaluation of inborn errors that cause or are associated with cobalamin or folate deficiency

Procedures

• Bone marrow aspiration and biopsy results are useful to confirm the diagnosis, to rule out myelodysplasia, and to assess the iron stores. Marrow is cellular with erythroid hyperplasia. Megaloblastic RBC precursors are abundant, and giant metamyelocytes are present. Iron stores may vary from high to low. The bone marrow begins to convert from megaloblastic to normoblastic within 12 hours, and normalization is complete within 2-3 days. Therefore, bone marrow aspiration should be performed as soon as possible and preferably before therapy if the procedure is considered useful for the patient's treatment.

Histologic Findings

Bone marrow is hypercellular. An increase in erythropoietic activity is reflected by a decreased or reversed myeloid-to-erythroid ratio. Erythroid precursors have megaloblastic features in that they are larger than normoblastic cells and they have immature nuclear development. Cytoplasmic maturation is normal, but nuclear remnants, Howell-Jolly bodies, may be present in the cytoplasm. Giant bands (neutrophils) may be present. Megakaryocytes may be large and hyperlobulated. Iron stores vary from being increased before therapy to decreased if iron is consumed during therapy for megaloblastosis. Bone marrow studies should be performed before therapy because therapy may restore normoblastic erythropoiesis rapidly.

TREATMENT

Section 6 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Medical Care

Most patients with megaloblastosis are treated with cobalamin and folate therapy to treat deficiencies in these substances. Transfusion therapy should be restricted to patients with severe, uncompensated, and life-threatening anemia. Because megaloblastic anemias usually develop gradually, most patients have adjusted to low Hgb levels and do not require transfusions.

• Cobalamin (1000 mcg) should be given parenterally daily for 2 weeks, then weekly until the hematocrit value is normal, and then monthly for life. This dose is large, but it may be required in some patients. Patients with neurological complications should receive cobalamin at 1000 mcg (more in some cases) every day for 2 weeks, then every 2 weeks for 6 months, and monthly for life.
  • Oral cobalamin (1000 mcg) can be administered to patients with hemophilia (to avoid intramuscular injections) and to patients with severe malnutrition or those who have abnormalities in the terminal ileum. Doses and schedules differ in recent publications. However, oral dosages should be monitored for desired response, since absorption can be variable and may be insufficient in some patients.
  • It may be practical to initially administer parenteral cobalamin to a patient with vitamin B-12 deficiency and then to continue treatment with oral cobalamin. Oral cobalamin is cost effective and better accepted by patients.
• Folate (1-5 mg) should be administered orally. If this is difficult, comparable doses can be administered parenterally.
• Therapeutic options when the etiology of megaloblastosis is uncertain include therapeutic doses of both cobalamin and folate after serum level measurements for cobalamin and folate levels, bone marrow, and other studies have been initiated. The Schilling test is not affected by previous therapy. Another option is to administer a trial of a physiological dose of folate. Cobalamin deficiency does not respond to daily folate doses of 100-400 mcg (physiological dose), but this dose results in complete response in patients with folate deficiency. Under no circumstances should therapeutic doses of folate (1-5 mg/d) be administered without cobalamin. The reason is that folate therapy corrects the anemia, but folate does not correct a cobalamin-induced neurological disorder and thus results in the progression of neuropsychiatric complications.
• Prophylactic folate therapy (1 mg/d) should be administered during pregnancy and the perinatal period to meet the increased demand for folate by the fetus and during lactation. Folate should also be given daily to patients with chronic hemolysis. Folate therapy is currently recommended for individuals with high levels of homocysteine who have a propensity for thromboembolic disease to prevent this complication. Multivitamins that contain folate have been recommended for elderly persons.
• • Fortification of foods with folic acid has been recommended to prevent hyperhomocysteinemia-related thrombosis, folate deficiency–related neoplasia, and pregnancy-related fetal abnormalities.
  • However, opponents to the fortification plan are concerned that folate-fortified foods given to patients with unrecognized cobalamin deficiencies will increase the frequency of cobalamin-induced neuropsychiatric disorders.
• Cobalamin therapy can be beneficial for patients with borderline cobalamin deficiency or in patients who present with only neuropsychiatric disorders. The role of minimal cobalamin deficiency in patients with borderline neuropsychiatric dysfunction has recently been recognized because of more sensitive tests and a greater awareness of this potential problem. One cause of borderline cobalamin deficiency is food-cobalamin malabsorption, described in the protein-bound absorption test discussion. Treatment with 50 mcg of oral cyanocobalamin daily can restore cobalamin stores in these patients.
• Blind loop syndrome should be treated with antibiotics.
• Patients with TCII deficiency may require higher doses of cobalamin.
• Tropical sprue should be treated with cobalamin and folate.
• Acute megaloblastic anemias due to nitrous oxide exposure can be treated with folate (5 mg/d) and cobalamin (1 mg IM).
• Fish tapeworm infection, pancreatitis, Zollinger-Ellison syndrome, and inborn errors should be treated with appropriate measures.

Consultations

• A hematologist should be consulted if the cause of the macrocytosis is not clear, if a patient does not respond adequately to therapy, and if neurological complications occur.
• A neurologist should be consulted for patients with potential neurological complications of cobalamin and folate deficiencies.
• A gastroenterologist should be consulted for the treatment of blind loop syndromes. In the case of diagnosed pernicious anemia, upper endoscopy should be performed to help rule out atrophic gastritis and because these patients are at greater risk of developing gastric carcinoma.
• A pediatrician with expertise in inborn errors should be consulted to help treat children with inborn errors.

Diet

• Patients should include rich sources of folate in their diets. Examples include asparagus, broccoli, spinach, lettuce, lemons, bananas, melons, liver, and mushrooms.
• To prevent loss of folate, foods should not be cooked excessively, especially in large amounts of water.
• To prevent cobalamin deficiency, patients who prefer vegetarian diets should include dairy products and eggs in their meals.

MEDICATION

Section 7 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

The goals of pharmacotherapy are to correct possible vitamin deficiencies, to prevent complications, and to reduce morbidity.

Drug Category: Vitamins

Cyanocobalamin (vitamin B-12) and folic acid are used to treat megaloblastic and macrocytic anemias secondary to deficiency. Both vitamin B-12 and folic acid are required for synthesis of purine nucleotides and metabolism of some amino acids. Each is essential for normal growth and replication. Deficiency of either cyanocobalamin or folic acid results in defective DNA synthesis and cellular maturation abnormalities. Consequences of deficiency are most evident in tissues with high cell turnover rates (eg, hematopoietic system).

FOLLOW-UP

Section 8 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Further Inpatient Care

• Patients should be monitored for response to therapy. Although patients may feel better as soon as therapy is started, monitoring the improvements with blood counts and clinical chemistry tests is important.
• • Elevated levels of LDH and indirect bilirubin will fall rapidly.
  • Reticulocytosis should be evident within 3-5 days and peaks in 4-10 days.
  • The Hgb level should rise approximately 1 g/wk. The rise of Hgb levels is valuable for monitoring a complete response. If the Hgb does not rise approximately 1 g/wk or is not normal within 2 months, other causes of anemia should be considered.
  • Leukocyte and platelets counts are usually restored to normal within days after therapy is started, but hypersegmented neutrophils may persist for 10-14 days.
  • A fall in the LDH level and reticulocytosis are excellent parameters of a response to therapy during the early phases.
  • Iron deficiency can be caused by the consumption of iron stores for the synthesis of new RBCs and may account for an incomplete response to therapy. Iron therapy may be indicated.
• Serum potassium levels can fall during therapy for severe cobalamin or folate deficiency and can lead to sudden death. Therefore, potassium supplements may be indicated.

Further Outpatient Care

• The response to therapy should monitored. A prolonged elevation of the LDH level can indicate that therapy has not corrected ineffective erythropoiesis, thus indicating a failure of therapy. Lack of an adequate rise in the Hgb level and the normalization of the Hgb level indicate that another cause of anemia may be present such as iron deficiency.
• Patients with neurological complications of cobalamin and folate deficiencies should be monitored for response to therapy.
• The development of gastric carcinoma should be evaluated periodically because this neoplasm may occur with increased frequency in patients with pernicious anemia.

Deterrence/Prevention

• Patients who have undergone either total or partial gastrectomies should receive lifelong monthly doses of cobalamin (1000 mcg IM).

Prognosis

• Prognosis is good if the etiology of megaloblastosis is identified and appropriate treatment is instituted. However, patients are at risk for complications of anemia, such as cardiac impairment and hypokalemia, during therapy for cobalamin deficiency.

Patient Education

• Patients with folate or cobalamin deficiency should receive dietary education on the choice of foods and instructions on how to prepare foods.
• Patients should know that goat milk contains little folate.

MISCELLANEOUS

Section 9 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Medical/Legal Pitfalls

• Failure to avoid treating patients with potential cobalamin deficiency with folate alone because this may lead to severe neuropsychiatric disease
• Failure to recognize and treat incipient neuropsychiatric impairment
• Failure to administer folate during pregnancies to avoid abnormal fetal development
• Failure to appropriately investigate macrocytosis

REFERENCES

Section 10 of 10

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

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• Bolaman Z, Kadikoylu G, Yukselen V, et al. Oral versus intramuscular cobalamin treatment in megaloblastic anemia: a single-center, prospective, randomized, open-label study. Clin Ther. Dec 2003;25(12):3124-34. [Medline].
• Carmel R. Malabsorption of food cobalamin. Baillieres Clin Haematol. Sep 1995;8(3):639-55. [Medline].
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• Remacha AF, Cadafalch J. Cobalamin deficiency in patients infected with the human immunodeficiency virus. Semin Hematol. Jan 1999;36(1):75-87. [Medline].
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• Tamura T, Picciano MF. Folate and human reproduction. Am J Clin Nutr. May 2006;83(5):993-1016.
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Article Last Updated: Jan 29, 2007